Voltage boosting circuit capable of modulating duty cycle automatically

ABSTRACT

The present invention relates to a voltage boosting circuit capable of modulating duty cycle automatically, which comprises an inductor, a switching module, and a control circuit. The inductor is coupled to an input for receiving an input power. The switching module is coupled among the inductor, a ground, and an output for switching so that the input power can charge the inductor and produce charged energy, or for switching so that the charged energy of the inductor can discharge to the output and produce an output voltage. The control circuit outputs at least a control signal according to the charged energy and the output voltage for controlling the switching module to switch the inductor and provide the input power to the output, to switch the charged energy of the inductor to discharge to the output, or to switch the input power to charge the inductor.

FIELD OF THE INVENTION

The present invention relates generally to a voltage boosting circuit,and particularly to a voltage boosting circuit capable of modulatingduty cycle automatically.

BACKGROUND OF THE INVENTION

Modern technologies are developing prosperously. Novel informationproducts are introduced frequently for satisfying people's variousneeds. Most of the early displays are cathode ray tube (CRT) displays.Owing to their huge size, tremendous power consumption, and radiationthreats to the health of long-term users, current commercial displaysare gradually replaced by liquid crystal displays (LCDs). LCDs have theadvantages of small size, low radiation, and low power consumption,making them become the mainstream in the market.

LCDs display images by controlling the transmissivity of liquid crystalcells according to data signals. Active-matrix LCDs adopt active controlof switching devices. Thereby, they are beneficial in displaying motionpictures. Thin film transistors (TFTs) are mainly applied to relateddevice of active-matrix LCDs.

Please refer to FIG. 1, which shows a schematic diagram of thedisplaying device according to the prior art. As shown in the figure,the displaying device comprises a display panel 10, a data drivingcircuit 14, and a charge pump 16. The data driving circuit 14 comprisesa plurality of digital-to-analog converting circuits (DAC) 141 and aplurality of operational amplifiers 143. The plurality ofdigital-to-analog converting circuits 141 produce a selecting voltageVsel to the plurality of operational amplifiers 143, respectively. Theplurality of operational amplifiers 143 generate a plurality of drivingsignals SL to a plurality of equivalent capacitors C of the displaypanel 10 according to the selecting voltage Vsel, respectively, fordriving the display panel to display images. The charge pump 16 isconnected to the differential circuits 1431 of the plurality ofoperational amplifiers 143 and the driving circuits simultaneously, andsupplies a fixed supply voltage VP to the differential circuits 1431 andthe driving circuits 1433 according to a reference voltage VDD to makethem operate.

According to the above description, the charge pump 16 of the displayingdevice according to the prior art provides the fixed supply voltage VPto the differential circuits 1431 and the driving circuits 1433, so thatthe operational amplifiers 143 can generate the plurality of drivingsignals SL. Nonetheless, the shortcoming of this method is that nomatter the voltage required by the plurality of equivalent capacitors Cof the display panel is greater or smaller than the reference voltageVDD, the charge pump 16 provides invariably the supply voltage VP to theplurality of operational amplifiers 143. Thereby, when no excessivelyhigh supply voltage VP is required, that excessively high supply voltageVP results in excess power consumption.

Accordingly, for solving the problem described above, the presentinvention provides a voltage boosting circuit capable of modulating dutycycle automatically, which supplies the power required by a loading bycharging and discharging an inductor and modulating the duty cycleautomatically according to the power required by the loading. Thereby,the purposes of reducing excess power consumption and saving power canbe achieved.

SUMMARY

An objective of the present invention is to provide a voltage boostingcircuit capable of modulating duty cycle automatically, which suppliesthe power required by a loading by charging and discharging an inductorand modulating the duty cycle automatically according to the powerrequired by the loading. Thereby, the purpose of saving power can beachieved.

Another objective of the present invention is to provide a voltageboosting circuit capable of modulating duty cycle automatically, whichjudges if the inductor in the voltage boosting circuit has completeddischarging according to the output current or output voltage of theinductor during discharging. Besides, the discharging time of theinductor is adjusted automatically according to the power required bythe loading for reducing the power consumption of the voltage boostingcircuit and achieving the purpose of saving power.

Still another objective of the present invention is to provide a voltageboosting circuit capable of modulating duty cycle automatically, whichjudges if the inductor in the voltage boosting circuit has completedcharging according to the charging current of the inductor duringcharging. Besides, the charging time of the inductor is adjustedautomatically according to the power required by the loading forreducing the power consumption of the voltage boosting circuit andachieving the purpose of saving power.

A further objective of the present invention is to provide a voltageboosting circuit capable of modulating duty cycle automatically, whichknows the charged energy stored in the inductor in the voltage boostingcircuit by detecting the output current of the inductor duringdischarging. Besides, the charging time of the inductor is adjustedautomatically according to the power required by the loading forreducing the power consumption of the voltage boosting circuit andachieving the purpose of saving power.

For achieving the purposes and effects described above, the presentinvention discloses a voltage boosting circuit capable of modulatingduty cycle automatically, which comprises an inductor, a switchingmodule, and a control circuit. The inductor has a first terminal and asecond terminal. The first terminal of the inductor is coupled to aninput for receiving an input power. The switching module is coupledamong the second terminal of the inductor, a ground, and an output ofthe voltage boosting circuit for switching and conducting the secondterminal of the inductor to the ground so that the input power cancharge the inductor and produce charged energy, or for switching andconducting the second terminal of the inductor to the output so that thecharged energy of the inductor can discharge to the output and producean output voltage. The control circuit outputs at least a control signalaccording to the capacity of the charged energy and the output voltagefor controlling the switching module to switch the inductor and providethe input power to the output, to switch the charged energy of theinductor to discharge to the output, or to switch the input power tocharge the inductor.

The present invention further discloses a voltage boosting circuitcapable of modulating duty cycle automatically, which comprises aninductor, a switching module, and a control circuit. The inductor has afirst terminal and a second terminal. The first terminal of the inductoris coupled to a ground. The switching module is coupled among the secondterminal of the inductor, an input, and an output of the voltageboosting circuit for switching and conducting the second terminal of theinductor to the input so that the inductor can receive the input powerfor charging and producing charged energy, or for switching andconducting the second terminal of the inductor to the output so that thecharged energy of the inductor can discharge to the ground and producean output voltage. The control circuit outputs at least a control signalaccording to the capacity of the charged energy and the output voltagefor controlling the switching module to switch the output to dischargeto the ground, to switch the charged energy of the inductor to dischargeto the ground, or to switch the input power to charge the inductor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic diagram of the displaying device according tothe prior art;

FIG. 2 shows a schematic diagram of the displaying device according apreferred embodiment of the present invention;

FIG. 3 shows a circuit diagram of the operational amplifier according toa preferred embodiment of the present invention;

FIG. 4 shows a circuit diagram of the voltage boosting circuit capableof modulating duty cycle automatically according to the first embodimentof the present invention;

FIG. 5 shows a waveform of the charging current of the inductoraccording to the present invention;

FIG. 6 shows waveforms of the voltage boosting circuit capable ofmodulating duty cycle automatically according to the first embodiment ofthe present invention;

FIG. 7 shows a circuit diagram of the voltage boosting circuit capableof modulating duty cycle automatically according to the secondembodiment of the present invention;

FIG. 8 shows waveforms of the voltage boosting circuit capable ofmodulating duty cycle automatically according to the third embodiment ofthe present invention;

FIG. 9 shows a circuit diagram of the voltage boosting circuit capableof modulating duty cycle automatically according to the fourthembodiment of the present invention;

FIG. 10 shows waveforms of the voltage boosting circuit capable ofmodulating duty cycle automatically according to the fourth embodimentof the present invention;

FIG. 11 shows a circuit diagram of the voltage boosting circuit capableof modulating duty cycle automatically according to the fifth embodimentof the present invention;

FIG. 12 shows waveforms of the voltage boosting circuit capable ofmodulating duty cycle automatically according to the fifth embodiment ofthe present invention;

FIG. 13 shows a circuit diagram of the voltage boosting circuit capableof modulating duty cycle automatically according to the sixth embodimentof the present invention;

FIG. 14 shows waveforms of the voltage boosting circuit capable ofmodulating duty cycle automatically according to the seventh embodimentof the present invention;

FIG. 15 shows a circuit diagram of the voltage boosting circuit capableof modulating duty cycle automatically according to the eighthembodiment of the present invention; and

FIG. 16 shows waveforms of the voltage boosting circuit capable ofmodulating duty cycle automatically according to the eighth embodimentof the present invention.

DETAILED DESCRIPTION

In the specifications and subsequent claims, certain words are used forrepresenting specific devices. A person having ordinary skill in the artshould know that hardware manufacturers might use different nouns tocall the same device. In the specifications and subsequent claims, thedifferences in names are not used for distinguishing devices. Instead,the differences in functions are the guidelines for distinguishing. Inthe whole specifications and subsequent claims, the word “comprising” isan open language and should be explained as “comprising but not limitedto”. Beside, the word “couple” includes any direct and indirectelectrical connection. Thereby, if the description is that a firstdevice is coupled to a second device, it means that the first device isconnected electrically to the second device directly, or the firstdevice is connected electrically to the second device via other deviceor connecting means indirectly.

In order to make the structure and characteristics as well as theeffectiveness of the present invention to be further understood andrecognized, the detailed description of the present invention isprovided as follows along with embodiments and accompanying figures.

Please refer to FIG. 2, which shows a schematic diagram of thedisplaying device according a preferred embodiment of the presentinvention. As shown in the figure, the displaying device comprises adisplay panel 20, a data driving circuit 24, and a voltage boostingcircuit 26. The data driving circuit 24 comprises a plurality ofdigital-to-analog converting circuits (DAC) 241 and a plurality ofoperational amplifiers 243. The plurality of digital-to-analogconverting circuits 241 produce a selecting voltage Vsel to theplurality of operational amplifiers 243, respectively. The plurality ofoperational amplifiers 243 generate a plurality of driving signals SL toa plurality of equivalent capacitors C of the display panel 20 accordingto the selecting voltage Vsel, respectively, for driving the displaypanel to display images. The voltage boosting circuit 26 is connected tothe driving circuits 2433 of the plurality of operational amplifiers 243only and supplies a supply voltage VP₁ to the driving circuits 2433 tomake them operate; the voltage boosting circuit 26 is connected todifferential circuits 2431. In addition, the differential circuits 2431of the operational amplifiers 243 and the digital-to-analog convertingcircuits 241 operate according to other power supplies.

Please refer to FIG. 3, which shows a circuit diagram of the operationalamplifier according to a preferred embodiment of the present invention.As shown in the figure, the differential circuit 2431 of the operationalamplifier 243 comprises a plurality of transistors M₁˜M₄ coupled to avoltage boosting unit 28 and a current source CS₁ and outputting asupply voltage VP₂ and the selecting voltage Vsel according to thevoltage boosting unit 28 for producing a differential voltage Vd. Thedriving circuit 2433 of the operational amplifier 243 comprises atransistor M₅ coupled to a voltage boosting unit 26 and a current sourceCS₂ and producing the driving signal SL according to the supply voltageVP₁ output by the voltage boosting unit 26 and the differential voltageVd for driving the display panel 20 to display images. Accordingly, thevoltage circuit 26 is coupled to the driving circuits 2433 of theoperational amplifiers 243 only but not to the differential circuits2431.

Besides, when the operational amplifier 243 generates the driving signalSL, the differential circuit 2431 outputs the differential signal Vd tothe transistor M₅ and turns on the transistor M₅. Then the supplyvoltage VP₁ can be provided directly to the driving signal SL to enablethe level of the driving signal SL output by the operational amplifier243 to reach the level required by the loading (for example, theplurality of equivalent capacitors C of the display panel 20).

Please refer to FIG. 4, which shows a circuit diagram of the voltageboosting circuit capable of modulating duty cycle automaticallyaccording to the first embodiment of the present invention. As shown inthe figure, the voltage boosting circuit 26 comprises an inductor L, aswitching module, and a control circuit. A first terminal of theinductor L is coupled to an input of the voltage boosting circuit 26 forreceiving an input power V_(DD). The switching module is used forswitching and conducting the second terminal of the inductor L to theground GND so that the input power V_(DD) can charge the inductor L andproduce charged energy, or for switching and conducting the secondterminal of the inductor L to the output of the voltage boosting circuit26 so that the charged energy of the inductor L can discharge to theoutput and produce an output voltage V_(OUT). The control circuitoutputs at least a control signal according to the capacity of thecharged energy and the output voltage V_(OUT) for controlling theswitching module to switch the inductor L and provide the input powerV_(DD) to the output, to switch the charged energy of the inductor L todischarge to the output, or to switch the input power V_(DD) to chargethe inductor L. The output voltage V_(OUT) can be used as, but notlimited to, the supply voltage VP₁ in FIG. 3.

According to the present embodiment, the switching module comprises aplurality of switches SW₁, SW₂. The switch SW₁ is coupled between thesecond terminal of the inductor L and the ground GND and connectselectrically the second terminal of the inductor L to the ground GNDaccording to a switching signal S₁ of the control signal.

The switch SW₂ is coupled to the second terminal of the inductor L andthe output of the voltage boosting circuit 26 and connects electricallythe second terminal of the inductor L to the output of the voltageboosting circuit 26 according to a switching signal S₂ of the controlsignal. The control circuit comprises a current detecting unit 261, anoutput-voltage detecting unit 263, and a control unit 265. The currentdetecting unit 261 is used for detecting an output current I_(O) betweenthe second terminal of the inductor L and the output of the voltageboosting circuit 26 for knowing the capacity of the charged energy inthe inductor L. The current detecting unit 261 also generates a currentdetecting signal IS according to the output current I_(O). In otherwords, the current detecting unit 261 detects the output current I_(O)for generating the current detecting signal IS. The output-voltagedetecting unit 263 is used for detecting the output voltage V_(OUT) andgenerates an output-voltage detecting signal VOS according to the outputvoltage V_(OUT). The control unit 265 receives the current detectingsignal IS and the output-voltage detecting signal VOS and outputs thecontrol signal according to the current detecting signal IS and theoutput-voltage detecting signal VOS. The control signal includes theswitching signals S₁, S₂. Namely, the control unit 265 controls theswitching of the switching signals S₁, S₂ according to the currentdetecting signal IS and the output-voltage detecting signal VOS.

Please refer to FIG. 5, which shows a waveform of the charging currentof the inductor according to the present invention. As shown in thefigure, when the inductor L is being charged, the inductor L starts tostore the charged energy. In other words, a current I_(L), as shown inFIG. 4, starts to increase gradually until the rated value of thecharged energy of the inductor L. When the inductor L startsdischarging, at the transient of discharging, an extremely high voltagewill occur across the inductor L. If a discharge path appears, thecharged energy stored in the inductor L will start to be released viathe discharge path. That is to say, the stored current in the inductor Lwill start to decrease gradually until the stored current is releasedcompletely. Thereby, according to the present embodiment, by using thecharacteristics of the inductor L, this current I_(L) (which isconverted to the output current I_(O) in FIG. 4) is detected for judgingif the inductor L has completed discharging. Then the discharging timeof the inductor can be adjusted automatically according to the powerrequired by the loading for reducing the power consumption of thevoltage boosting circuit and saving power. In the following, how tomodule the duty cycle by means of the characteristics of the inductor Lfor supplying the power required by the loading is described in details.

Please refer to FIG. 6, which shows waveforms of the voltage boostingcircuit capable of modulating duty cycle automatically according to thefirst embodiment of the present invention. As shown in the figure,initially, because the output voltage V_(OUT) is lower than the inputpower V_(DD), the control unit 265 outputs the low-level switchingsignal S₁ and the high-level switching signal S₂ for turning off theswitch SW₁ and turning on the switch SW₂. Thereby, in the time T₁, theinput power V_(DD) is output directly to the output and producing theoutput voltage V_(OUT). For the embodiment in FIGS. 2 and 3, the outputvoltage V_(OUT) is used as the supply voltage VP₁ and is converted tothe driving signal SL by the driving circuit 2433 for charging theequivalent capacitor C of the display panel 20. Thereby, the outputvoltage V_(OUT) will be charged to the level of the input power V_(DD).

Next, when the output voltage V_(OUT) is charged to the level of theinput power V_(DD), because the voltage levels of the input and theoutput are identical, there will be no current flowing through. Hence,the output current I_(O) detected by the current detecting unit 261 is 0A, and the current detecting unit 261 outputs the high-level currentdetecting signal IS to make the control unit 265 output the high-levelswitching signal S₁ and the low-level switching signal S₂ for turning onthe switch SW₁ and turning off the switch SW₂. Then the input powerV_(DD) charges the inductor L for a charging time T_(C1) to store thecharged energy to the inductor L. As the charging is finished, theswitching signal S_(r) is changed to low and the switching signal S₂ ischanged to high for turning off the switch SW₁ and turning on the switchSW₂. In the discharging time T_(DC1), the charged energy in the inductorL starts to discharge to the output; at the transient when the switchSW₁ is turned off the voltage level at the node P will increase rapidly.When the switch SW₂ is turned on, the charged energy in the inductor Lstarts to discharge to the output and decreases gradually as dischargingto the output. As the inductor L discharges, the output voltage at theoutput V_(OUT) is charged gradually and increases. In addition,according to the Lenz's Law, when the inductor L is dischargedcompletely, namely, when the output current I_(O) is zero, the voltagelevel at the node P will be identical to the level of the output voltageV_(OUT) which is 1.5 times the input power V_(DD) according to thepresent embodiment. In practice, the voltage level at the node P isdetermined by the inductance of the inductor L and the loading at theoutput.

When the voltage level at the node P is identical to the level of theoutput voltage V_(OUT), the output current I_(O) detected by the currentdetecting unit 261 is 0 A, which makes the control unit 265 to turn onthe switch SW₁ and turn off the switch SW₂ via the switching signals S₁,S₂. Then the input power V_(DD) charges the inductor L for a chargingtime T_(C2). After charging, the switching signal S₁ is changed to lowand the switching signal S₂ is changed to high for turning off theswitch SW₁ and turning on the switch SW₂. Afterwards, in a dischargingtime T_(DC2), the inductor L discharges to the output. According to thepresent embodiment, a predetermined voltage is 1.8 times the input powerV_(DD). Thereby, when the output voltage increases to greater than 1.8times the input power V_(DD), the output-voltage detecting unit 263outputs the high-level output-voltage detecting signal VOS, which makesthe control unit 265 to output low-level switching signals S₁, S₂simultaneously for turning off the switches SW₁, SW₂ at the same time.Then the charging and discharging of the voltage boosting circuit 26 isstopped and entering a stop time T₂.

In the stop time T₂, the voltage boosting circuit 26 does not charge ordischarge. If there is power consumption at the output, the outputvoltage V_(OUT) will decrease gradually. As the output voltage V_(OUT)is lower than the predetermined voltage, the output-voltage detectingunit 263 changes the output-voltage detecting signal VOS to lowaccording to the output voltage V_(OUT). Thereby, the switching signalS₁ is changed to high and the switching signal S₂ is kept low forturning on the switch SW₁ and turning off the switch SW₂. After theinput power V_(DD) restarts charging the inductor L for a charging timeT_(C3), the switching signal S₁ is changed to low and the switchingsignal S₂ is kept high and entering a discharging time T_(DC3), in whichthe inductor L discharges to the output until the output voltage V_(OUT)is higher than the predetermined voltage again. Then, the output-voltagedetecting signal VOS is changed to high for turning off the switchesSW₁, SW₂ again.

According to the above description, the voltage boosting circuit 26according to the present embodiment uses the fixed predeterminedcharging times T_(C1), T_(C2), T_(C3) to charge the inductor L to thesame charged energy. In addition, in each of the discharging timesT_(DC1), T_(DC2), T_(DC3), the charge energy is discharged completely tothe output. As the output voltage V_(OUT) increases gradually, each ofthe discharging times T_(DC1), T_(DC2), T_(DC3) becomes shorter.Moreover, the following equation can be given:

$\begin{matrix}{\frac{V_{OUT}}{V_{DD}} = {\frac{TS}{{TS}_{1\; {off}}} = \frac{1}{1 - D}}} & (1)\end{matrix}$

TS is the period of each charging-discharging cycle and equal to, forexample, T_(C1)+T_(DC1) or T_(C2)+T_(DC2). TS_(1off) is the dischargingtime corresponding to the charging-discharging cycle TS, for example,T_(DC1) or T_(DC2). D is the percentage of charging time in eachcharging-discharging cycle. For example, D is the percentage of T_(C1)in T_(C1)+T_(DC1).

Please refer to FIG. 7, which shows a circuit diagram of the voltageboosting circuit capable of modulating duty cycle automaticallyaccording to the second embodiment of the present invention. Thedifference between the present embodiment and the first embodiment isthat the current detecting unit 261 of the control circuit according tothe present embodiment is coupled between the second terminal of theinductor L and the node P. The rest is the same as the first embodiment.Hence, the details will not be described again.

Because the current flowing through the inductor L increases as thestored charged energy increases, as shown in FIG. 5, according to thepresent embodiment, a charging current I_(C) flowing through theinductor L is detected in the charging time T_(C1), T_(C2), or T_(C3)for judging if charging of the inductor L has completed. This isdifferent from the first embodiment, in which the charging times T_(C1),T_(C2), T_(C3) are predetermined to be identical. The waveforms of thepresent embodiment are the same as those in FIG. 6. In the time T₁ orthe discharging times T_(DC1), T_(DC2), T_(DC3), as in the firstEmbodiment, the switch SW₁ is turned off and the switch SW₂ is turnedon. Thereby, the current detecting unit 261 detects the output currentI_(O) for judging if the inductor L has completed discharging. In thecharging time T_(C1), T_(C2), or T_(C3), because the switch SW₁ isturned on and the switch SW₂ is turned off, the current detecting unit261 changes to detect the charging current I_(C). When the chargingcurrent I_(C) is higher than a predetermined value, the currentdetecting unit 261 outputs the low-level current detecting signal IS,which makes the control unit 265 to turn off the switch SW₁ and turn onthe switch SW₂ for finishing the charging time T_(C1), T_(C2), orT_(C3).

Please refer to FIG. 8, which shows waveforms of the voltage boostingcircuit capable of modulating duty cycle automatically according to thethird embodiment of the present invention. The circuit diagram accordingto the present embodiment is the same as FIG. 6 according to the secondembodiment. The difference is that the discharging times T_(DC1),T_(DC2), T_(DC3) are predetermined and fixed. In addition, the currentdetecting unit 261 detects the current value of the output current I_(O)when the discharging times T_(DC1), T_(DC2), T_(DC3) are finished forknowing if the charged energy stored in the inductor L during theprevious charging time T_(C1), T_(C2), or T_(C3) is too much or too few.If so, the predetermined value of the current detecting unit 261 isadjusted for further adjusting the charging time.

As shown in the figure, when the time T₁ is passed and the outputvoltage V_(OUT) is charged to the level of the input power V_(DD), thecurrent detecting unit 261 detects that the output current I_(O) is 0 Aand outputs the high-level current detecting signal IS, which makes thecontrol unit 265 output the high-level switching signal S₁ and thelow-level switching signal S₂ for turning on the switch SW₁ and turningoff the switch SW₂ and entering the charging time T_(C1) to charge theinductor L by the input power V_(DD). When the charging current I_(C) ishigher than the predetermined value, it means completion of charging:the current detecting unit 261 outputs the low-level current detectingsignal IS to the control unit 265 to make the control unit 265 outputthe low-level switching signal S₁ and the high-level switching signal S₂for turning off the switch SW₁ and turning on the switch SW₂ andentering the discharging time T_(DC1). After the fixed and predetermineddischarging time T_(DC1), the current detecting unit 261 adjusts itspredetermined value according to the output current I_(O) at the moment.According to the present embodiment, the output current I_(O) after thedischarging time T_(DC1) is smaller than a threshold value of thecurrent detecting unit 261, which means that the charged energy storedin the inductor L during the charging time T_(C1) is too few. Thereby,the predetermined value of the current detecting unit 261 is adjustedhigher, namely, increasing the next charging time T_(C2).

Because the predetermined value of the current detecting unit 261 isadjusted higher, the charging time T_(C2) will be longer than thecharging time T_(C1), making the charged energy stored in the inductor Lmore. After the charging time T_(C2) is finished, the discharging timeT_(DC2) starts. As the output voltage V_(OUT) is higher than thepredetermined voltage, 1.8 times the input power V_(DD), theoutput-voltage detecting unit 263 also outputs the high-leveloutput-voltage detecting signal VOS for turning off the switches SW₁,SW₂ simultaneously and entering the stop time T₂. When the outputvoltage V_(OUT) decreases below the predetermined voltage, the outputvoltage-detecting signal VOS is changed to low for turning on the switchSW₁ and turning off the switch SW₂ and entering the charging timeT_(C3). Then the input power V_(DD) will charge the inductor L again.

According to the above description, the voltage boosting circuit 26according to the present embodiment uses the fixed predetermineddischarging times T_(DC1), T_(DC2), T_(DC3) to discharge the inductor Lto the output. When the discharging time T_(DC1), T_(DC2), or T_(DC3) isfinished, the current detecting unit 261 is used for detecting theoutput current I_(O). If the output current I_(O) is greater than thethreshold value, it means that the charging time is too long and thecharged energy is too much. Then the predetermined value of the currentdetecting unit 261 is adjusted lower. If the output current I_(O) issmaller than the threshold value, it means that the charging time is tooshort and the charged energy is too few. Then the predetermined value ofthe current detecting unit 261 is adjusted higher for adjusting thecharging time of the inductor L.

When the threshold value of the current detecting unit 261 is set to 0 Aand the discharging time T_(DC1), T_(DC1), T_(DC2) or T_(DC3) isfinished, if there is still the output current I_(O), it means that thecharging time is too long and the charged energy is too much; if thereis no output current I_(O), it means that the charging time is too shortand the charged energy is too few.

Please refer to FIGS. 9 and 10. FIG. 9 shows a circuit diagram of thevoltage boosting circuit capable of modulating duty cycle automaticallyaccording to the fourth embodiment of the present invention; FIG. 10shows waveforms of the voltage boosting circuit capable of modulatingduty cycle automatically according to the fourth embodiment of thepresent invention. The difference between the present embodiment and thefirst embodiment is that according to the present embodiment, a voltagedetecting unit 262 replaces the current detecting unit 261 according tothe first embodiment. The rest circuit and principle are the same as thefirst embodiment. Hence, the details will not be described again.

As shown in the figure, the voltage detecting unit 262 is coupled to thenode P and the output. After the time T₁, when the output voltageV_(OUT) is charged to the level of the input power V_(DD), because thevoltage levels of the input and the output of the voltage boostingcircuit 26 are identical, there will be no current passing between thetwo nodes. Accordingly, the voltage detecting unit 262 will detect novoltage difference between the node P and the output and output thehigh-level voltage detecting signal VS, which makes the control unit 265to output the high-level switching signal S₁ and the low-level switchingsignal S₂ for turning on the switch SW₁ and turning off the switch SW)and entering the charging time T_(C1). Besides, as described in thefirst embodiment, after the discharging time T_(DC1) and discharging ofthe charged energy in the inductor L to the output has finished, thevoltage level of the node P is equal to the output voltage V_(OUT).Thereby, the voltage detecting unit 262 will also detect no voltagedifference between the node P and the output and output the high-levelvoltage detecting signal VS. The rest can be deduced by analogy.According to the above description, the first embodiment uses the methodof detecting current, while the present embodiment uses the method ofdetecting voltage for judging if discharging of the inductor L hasfinished or not.

Please refer to FIGS. 11 and 12. FIG. 11 shows a circuit diagram of thevoltage boosting circuit capable of modulating duty cycle automaticallyaccording to the fifth embodiment of the present invention; FIG. 12shows waveforms of the voltage boosting circuit capable of modulatingduty cycle automatically according to the fifth embodiment of thepresent invention. As shown in FIG. 11, the difference between thepresent embodiment and the first embodiment is the connection of theinductor L with and switching module. The first terminal of the inductorL is coupled to the ground GND; the switch SW₁ of the switching moduleis coupled between the input power V_(DD) and the second terminal of theinductor L. The rest is the same as the first embodiment.

As shown in FIG. 12, initially, the level of the output voltage V_(OUT)is unknown. It could be any level between the input power V_(DD) and theground GND. Assuming that the output voltage V_(OUT) is equal to theinput power V_(DD), which is greater than the level of the ground GNS(0V), the control unit 265 will output the low-level switching signal S₁and the high-level switching signal S₂ for turning off the switch SW₁and turning on the switch SW₂. Consequently, in the time T₁, the outputwill discharge to the ground GND via the inductor L, and thus making theoutput voltage V_(OUT) decrease to 0V of the ground GND. At this moment,because the voltage levels of the output and the ground GND areidentical, there will be no current flowing between the two nodes.Hence, the current detecting unit 261 will detect the output currentI_(O) to be 0 A and output the high-level current detecting signal IS,which makes the control unit 265 output the high-level switching signalS₁ and the low-level switching signal S₂ for turning on the switch SW₁and turning off the switch SW₂. Thereby, the input power V_(DD) willcharge the inductor L for the charging time T_(C1) for producing thecharged energy.

After charging is finished, the switching signal S₁ is changed to lowand the switching signal S₂ is changed to high for turning off theswitch SW₁ and turning on the switch SW₂ and entering the dischargingtime T_(DC1). At this moment, the first terminal of the inductor L iscoupled to the ground GND and the second terminal thereof generates anegative voltage. At the transient when the switch SW₂ is turned on, theoutput will discharge to the ground GND via the switch SW₂ and theinductor L. The voltage across the inductor L will increase rapidly andthen decrease gradually as discharging to the ground GND proceeds. Theoutput voltage V_(OUT) of the output will also decrease gradually. Inaddition, like in the first embodiment, after discharging of theinductor L is finished, namely, when the output current I_(O) is zero,the voltage level of the node P will be equal to the level of the outputvoltage V_(OUT), which is equal to minus 0.5 times the input powerV_(DD).

When the voltage level of the node P is equal to the level of the outputvoltage V_(OUT), the current detecting unit 261 detects the outputcurrent I_(O) to be 0 A, which makes the control unit 265 to turn on theswitch SW₁ and turn off the switch SW₂ using the switching signals S₁,S₂. Then the input power V_(DD) charges the inductor L for the chargingtime T_(C2). After charging is finished, the switching signal S₁ ischanged to low and the switching signal S₂ is changed to high forturning off the switch SW₁ and turning on the switch SW₂ and enteringthe discharging time T_(DC2), in which the inductor L discharges to theground GND. Because the predetermined voltage according to the presentembodiment is minus 0.8 times the input power V_(DD), as the outputvoltage V_(OUT) decreases below minus 0.8 times the input power V_(DD),the output-voltage detecting unit 263 outputs the high-leveloutput-voltage detecting signal VOS to make the control unit 265 outputthe low-level switching signals S₁, S₂ simultaneously for turning offthe switches SW₁, SW₂ at the same time. Thereby, charging anddischarging of the voltage boosting circuit 26 are stopped and enteringthe stop time T₂.

In the stop time T₂, the voltage boosting circuit 26 does not charge ordischarge. Hence, if there is power consumption at the output, theoutput voltage V_(OUT) will increase gradually. When the output voltageV_(OUT) is higher than the predetermined voltage, the output-voltagedetecting unit 263 changes the output-voltage detecting signal VOS tolow according to the output voltage V_(OUT). Thereby, the switchingsignal S₁ is changed to high and the switching signal S₂ is kept low forturning on the switch SW₁ and turning off the switch SW₂. After theinput power V_(DD) restarts to charge the inductor L for the chargingtime T_(C3), the switching signal S₁ is changed to low and the switchingsignal S₂ is changed to high and entering the discharging time T_(DC3),in which the inductor L discharges to the ground GND until the outputvoltage V_(OUT) is lower than the predetermined voltage again. Then theoutput-voltage detecting signal VOS is changed to high for turning offthe switches SW₁, SW₂ again.

According to the above description, the principle of the voltageboosting circuit 26 according to the present embodiment is the same asthat according to the first embodiment, in which the fixed predeterminedcharging times T_(C1), T_(C2), T_(C3) are used to charge the inductor Lto the same charged energy. In addition, in each of the dischargingtimes T_(DC1), T_(DC2), T_(DC3), the charge energy is dischargedcompletely to the ground GND and decreasing the output voltage V_(OUT)gradually. As the output voltage V_(OUT) decreases, each of thedischarging times T_(DC1), T_(DC2), T_(DC3) becomes shorter. Inaddition, by using the connection of the inductor L and the switch SW₁according to the present embodiment, the output voltage V_(OUT) at theoutput can be negative.

Please refer to FIG. 13, which shows a circuit diagram of the voltageboosting circuit capable of modulating duty cycle automaticallyaccording to the sixth embodiment of the present invention. The presentembodiment combines the second and fifth embodiments. According to thepresent embodiment, the current detecting unit 261 of the controlcircuit is coupled between the second terminal of the inductor L and thenode P.

Like the second embodiment, according to the present embodiment, thecharging current I_(C) flowing through the inductor L is detected in thecharging time T_(C1), T_(C2), or T_(C3) for judging if charging of theinductor L has completed. This is different from the fifth embodiment,in which the charging times T_(C1), T_(C2), T_(C3) are predetermined.The waveforms according the present embodiment are the same as FIG. 12.In the time T₁ or the discharging times T_(DC1), T_(DC2), T_(DC3), likethe fifth embodiment, the switch SW₁ is turned off and the switch SW₂ isturned on. Hence, the current detecting unit 261 detects the outputcurrent I_(O) for judging if charging of the inductor L has completed.In the charging times T_(C1), T_(C2), T_(C3), because the switch SW₁ isturned on and the switch SW₂ is turned off, the current detecting unit261 changes to detect the charging current I_(C). As the chargingcurrent I_(C) is higher than the predetermined value, the currentdetecting unit 261 outputs the low-level current detecting signal IS formaking the control unit 265 turn off the switch SW₁ and turn on theswitch SW₂ for finishing the charging time T_(C1), T_(C2), or T_(C3).

Please refer to FIG. 14, which shows waveforms of the voltage boostingcircuit capable of modulating duty cycle automatically according to theseventh embodiment of the present invention. The circuit diagramaccording to the present embodiment is identical to FIG. 13 according tothe sixth embodiment. The difference is that the discharging timesT_(DC1), T_(DC2), T_(DC3) according to the present embodiment arepredetermined and fixed. Besides, the current detecting unit 261 is usedfor the output current I_(O) when the discharging times T_(DC1),T_(DC2), T_(DC3) are finished for knowing that the charged energy storedin the inductor L is too much or too few. If the charged energy is toomuch or too few, the predetermined value of the current detecting unit261 is adjusted and thus further adjusting the charging time. Theprinciple of this part is like the third embodiment. The voltageboosting circuit 26 according to the present embodiment enables theinductor L to discharge to the output in fixed and predetermineddischarging times T_(DC1), T_(DC2), T_(DC3). When the discharging timesT_(DC1), T_(DC2), T_(DC3) are finished, the current detecting unit 261is used for detecting the output current I_(O). If the output currentI_(O) is greater than the threshold value, it means that the chargingtime is too long and the charged energy is too much; if the outputcurrent I_(O) is smaller than the threshold value, it means that thecharging time is too short and the charged energy is too few. Then thepredetermined value of the current detecting unit 261 is adjusted lower.If there is no output current I_(O), it means that the charging time istoo short and the charged energy is too few. Hence, the predeterminedvalue of the current detecting unit 261 is adjusted higher for adjustingthe charging time of the inductor L.

Please refer to FIGS. 15 and 16. FIG. 15 shows a circuit diagram of thevoltage boosting circuit capable of modulating duty cycle automaticallyaccording to the eighth embodiment of the present invention; FIG. 16shows waveforms of the voltage boosting circuit capable of modulatingduty cycle automatically according to the eighth embodiment of thepresent invention. The difference between the present embodiment and thefifth embodiment is that the voltage detecting unit 262 according to thepresent embodiment replaces the current detecting unit 261 according tothe fifth embodiment. The rest circuit and the principle are the same asthe fifth embodiment. Hence, the details will not be described again.

As shown in FIG. 16, after the time T₁, when the output voltage V_(OUT)is discharged to the level of the ground GND, because the voltage levelsof the output and the ground GND are the same, there will be no currentflowing between the two nodes. Accordingly, the voltage detecting unit262 will detect no voltage difference between the node P and the outputand output the high-level voltage detecting signal VS, which makes thecontrol unit 265 to output the high-level switching signal S₁ and thelow-level switching signal S₂ for turning on the switch SW₁ and turningoff the switch SW₂ and entering the charging time T_(C1). Besides, asdescribed in the fifth embodiment, after the discharging time T_(DC1)and discharging of the charged energy in the inductor L to the outputhas finished, the voltage level of the node P is equal to the outputvoltage V_(OUT). Thereby, the voltage detecting unit 262 will alsodetect no voltage difference between the node P and the output andoutput the high-level voltage detecting signal VS. The rest can bededuced by analogy.

To sum up, the voltage boosting circuit capable of modulating duty cycleautomatically according to the present invention knows whether theinductor has completed charging or discharging or whether the outputvoltage has reached the predetermined voltage by using the controlcircuit to detect the charged energy and the output voltage of theinductor. Then the switching module is controlled according to thedetection result to switch for switching the inductor automatically tocharge, discharge, or stop charging and discharging and thus modulatingthe duty cycle of the voltage boosting circuit automatically. Thereby,the purposes of reducing power consumption and saving power can beachieved.

Accordingly, the present invention conforms to the legal requirementsowing to its novelty, nonobviousness, and utility. However, theforegoing description is only embodiments of the present invention, notused to limit the scope and range of the present invention. Thoseequivalent changes or modifications made according to the shape,structure, feature, or spirit described in the claims of the presentinvention are included in the appended claims of the present invention.

1. A voltage boosting circuit capable of modulating duty cycleautomatically, comprising: an inductor, having a first terminal and asecond terminal, and said first terminal of said inductor coupled to aninput for receiving an input power; a switching module, coupled amongsaid second terminal of said inductor, a ground, and an output of saidvoltage boosting circuit, used for switching to conduct said secondterminal of said inductor and said ground for enabling said input powerto charge said inductor and producing charged energy, or used forswitching to conduct said second terminal of said inductor and saidoutput for enabling said charged energy of said inductor to discharge tosaid output and produce an output voltage; and a control circuit,outputting at least a control signal according to the capacity of saidcharged energy and said output voltage for controlling said switchingmodule to switch and enable said charged energy of said inductor todischarge to said output or controlling said switching module to switchand enable said input power to charge said inductor.
 2. The voltageboosting circuit of claim 1, wherein when said output voltage is lowerthan said input power, said control circuit controls said switchingmodule to switch said inductor for providing said input power to saidoutput.
 3. The voltage boosting circuit of claim 1, wherein when saidoutput voltage is higher than a predetermined voltage, said switchingmodule turns off the path between said second terminal of said inductorand said ground and the path between said second terminal of saidinductor and said output of said voltage boosting circuit according tosaid control signal.
 4. The voltage boosting circuit of claim 1, whereinsaid switching module comprises: a first switch, coupled between saidsecond terminal of said inductor and said ground, and turned onaccording to a first switching signal of said control signal forconnecting said second terminal of said inductor to said ground; and asecond switch, coupled between said second terminal of said inductor andsaid output of said voltage boosting circuit, and turned on according toa second switching signal of said control signal for connecting saidsecond terminal of said inductor to said output of said voltage boostingcircuit.
 5. The voltage boosting circuit of claim 1, wherein saidcontrol circuit comprises: a current detecting unit, detecting an outputcurrent between said second terminal of said inductor and said output ofsaid voltage boosting circuit for knowing the capacity of said chargedenergy, and generating a current detecting signal according to saidoutput current; an output-voltage detecting unit, detecting said outputvoltage, and generating an output-voltage detecting signal according tosaid output voltage; and a control unit, outputting said control signalaccording said current detecting signal and said output-voltagedetecting signal.
 6. The voltage boosting circuit of claim 1, whereinsaid control circuit comprises: a current detecting unit, detecting acharging current between said second terminal of said inductor and saidground, and generating a current detecting signal when said chargingcurrent is higher than a predetermined value; an output-voltagedetecting unit, detecting said output voltage, and generating anoutput-voltage detecting signal according to said output voltage; and acontrol unit, outputting said control signal according said currentdetecting signal and said output-voltage detecting signal.
 7. Thevoltage boosting circuit of claim 6, wherein when said charging currentis higher than said predetermined value, said current detecting unitoutputs said current detecting signal for enabling said control unit toturn on the path between said second terminal of said inductor and saidoutput of said voltage boosting circuit for finishing a charging time.8. The voltage boosting circuit of claim 6, wherein when said chargedenergy of said inductor discharges to said output for a dischargingtime, said current detecting unit detects an output current between saidsecond terminal of said inductor and said output of said voltageboosting circuit; if said output current is greater than a thresholdvalue, said current detecting unit adjusts said predetermined valuelower; and if said output current is less than or equal to saidthreshold value, said current detecting unit adjusts said predeterminedvalue higher.
 9. The voltage boosting circuit of claim 1, wherein saidcontrol circuit comprises: a voltage detecting unit, detecting if thevoltage level of said charged energy is equal to said output voltage,and generating a voltage detecting signal according to the voltage levelof said charged energy; an output-voltage detecting unit, detecting saidoutput voltage, and generating an output-voltage detecting signalaccording to said output voltage; and a control unit, outputting saidcontrol signal according said voltage detecting signal and saidoutput-voltage detecting signal.
 10. The voltage boosting circuit ofclaim 1, wherein said output voltage is output to a pixel capacitor of adisplay panel for driving said display panel.
 11. A voltage boostingcircuit capable of modulating duty cycle automatically, comprising: aninductor, having a first terminal and a second terminal, and said firstterminal of said inductor coupled to a ground; a switching module,coupled among said second terminal of said inductor, an input, and anoutput of said voltage boosting circuit, used for switching to conductsaid second terminal of said inductor and said input for enabling saidinductor to receive an input power and charge said inductor forproducing charged energy, or used for switching to conduct said secondterminal of said inductor and said output for enabling said chargedenergy of said inductor to discharge to said ground and produce anoutput voltage; and a control circuit, outputting at least a controlsignal according to the capacity of said charged energy and said outputvoltage for controlling said switching module to switch and enable saidoutput to discharge to said ground, controlling said switching module toswitch and enable said charged energy of said inductor to discharge tosaid ground, or controlling said switching module to switch and enablesaid input power to charge said inductor.
 12. The voltage boostingcircuit of claim 11, wherein when said output voltage is higher than thevoltage level of said ground, said control circuit controls saidswitching module to switch said output for discharging to said ground.13. The voltage boosting circuit of claim 11, wherein when said outputvoltage is lower than a predetermined voltage, said switching moduleturns off the path between said second terminal of said inductor andsaid input and the path between said second terminal of said inductorand said output of said voltage boosting circuit according to saidcontrol signal.
 14. The voltage boosting circuit of claim 11, whereinsaid switching module comprises: a first switch, coupled between saidsecond terminal of said inductor and said input, and turned on accordingto a first switching signal of said control signal for connecting saidsecond terminal of said inductor to said input; and a second switch,coupled between said second terminal of said inductor and said output ofsaid voltage boosting circuit, and turned on according to a secondswitching signal of said control signal for connecting said secondterminal of said inductor to said output of said voltage boostingcircuit.
 15. The voltage boosting circuit of claim 11, wherein saidcontrol circuit comprises: a current detecting unit, detecting an outputcurrent between said second terminal of said inductor and said output ofsaid voltage boosting circuit for knowing the capacity of said chargedenergy, and generating a current detecting signal according to saidoutput current; an output-voltage detecting unit, detecting said outputvoltage, and generating an output-voltage detecting signal according tosaid output voltage; and a control unit, outputting said control signalaccording said current detecting signal and said output-voltagedetecting signal.
 16. The voltage boosting circuit of claim 11, whereinsaid control circuit comprises: a current detecting unit, detecting acharging current between said input and said second terminal of saidinductor, and generating a current detecting signal when said chargingcurrent is higher than a predetermined value; an output-voltagedetecting unit, detecting said output voltage, and generating anoutput-voltage detecting signal according to said output voltage; and acontrol unit, outputting said control signal according said currentdetecting signal and said output-voltage detecting signal.
 17. Thevoltage boosting circuit of claim 16, wherein when said charging currentis higher than said predetermined value, said current detecting unitoutputs said current detecting signal for enabling said control unit toturn on the path between said second terminal of said inductor and saidoutput of said voltage boosting circuit for finishing a charging time.18. The voltage boosting circuit of claim 16, wherein when said chargedenergy of said inductor discharges to said ground for a dischargingtime, said current detecting unit detects an output current between saidsecond terminal of said inductor and said output of said voltageboosting circuit; if said output current is greater than a thresholdvalue, said current detecting unit adjusts said predetermined valuelower; and if said output current is less than or equal to saidthreshold value, said current detecting unit adjusts said predeterminedvalue higher.
 19. The voltage boosting circuit of claim 11, wherein saidcontrol circuit comprises: a voltage detecting unit, detecting if thevoltage level of said charged energy is equal to said output voltage,and generating a voltage detecting signal according to the voltage levelof said charged energy; an output-voltage detecting unit, detecting saidoutput voltage, and generating an output-voltage detecting signalaccording to said output voltage; and a control unit, outputting saidcontrol signal according said voltage detecting signal and saidoutput-voltage detecting signal.